In the field of ultrasonic diagnosis, for example, the elastography diagnosis of diagnosing hardness is performed in actual medical practice. Elastography diagnosis is the diagnostic method of diagnosing that a given tissue is harder than a normal region because of hepatic cirrhosis or fibrosis or calcification of the tissue. In general, an examiner irradiates an object with ultrasonic waves while repeatedly pressing and releasing the object by moving an ultrasonic probe with his/her hand. Diagnosis of hardness is performed by analyzing reflected waves from a living tissue. The method of repeating such pressing and releasing action has problems, for example, that measured values vary depending on the way of moving the probe and different examiners obtain different results.
Recently, attention has been paid to a technique called shear wave elastography. First of all, shear waves are generated from a living body by irradiating an object with relatively strong ultrasonic waves (push pulses) from an ultrasonic probe. The propagation velocity of the shear waves is measured with tracking pulses output from the ultrasonic probe. The result is analyzed and visualized. The resultant image is then superimposed on a B-mode image to perform diagnosis of hardness. Unlike general elastography, shear wave elastography needs not repeat pressing and releasing action, and hence can implement measurement with more ease and higher reproducibility.
To generate such push pulses in shear wave elastography, a driving pulse string (driving signal) having a high peak value of 100 V or the like is used. An applied high voltage (for example, 100 V) is required to generate a driving pulse string having a high peak value. If, however, a high voltage is applied to a pulser, a transmission power source lacks in charge (that is, charge accumulated in the capacitor in the transmission power source). This often leads to a droop in applied voltage (a drop in voltage) to the pulser relative to the set voltage (open voltage) of the transmission power source.
On the other hand, in the field of ultrasonic diagnosis, for example, a DDS (Drug Delivery System) is used in actual medical practice. In this system, a drug capsule is administered to an object in advance, and an operator such as a doctor intentionally breaks the drug capsule in the body by irradiating the capsule with relatively strong ultrasonic waves from an ultrasonic probe of an ultrasonic diagnostic apparatus. It is then possible to quantitatively and spatially control the internal distribution of the drug in the object by using the breakage of the capsule. In addition, using an ultrasonic diagnostic apparatus can simultaneously perform diagnosis and the breakage of a drug capsule.
In the use of a drug delivery system, a driving pulse string having a high peak value is used even when such relatively strong ultrasonic waves are applied. To generate a driving pulse string having a high peak value, an applied high voltage (for example, 100 V) is required. For this reason, like the above shear wave elastography, the above technique has often the problem of the occurrence of voltage droops.